The present invention relates to fluid infusion systems, and more particularly to an improved apparatus and method for infusing fluid into the human body.
The infusion of fluids such as parenteral solutions and blood into the human body is usually accomplished by means of an administration set in conjunction with appropriate flow metering means to control the rate of fluid flow through the set. One form of flow metering means which is potentially attractive for this application is the peristaltic-type pump, which operates to repeatedly compress and expand a section of tubing so as to cause fluid to flow through the tubing at a controlled rate. Unfortunately, the operation of such peristaltic-type pumps in connection with administration sets has not been entirely satisfactory because of metering inaccuracies brought about by the partially non-resilient characteristic of the vinyl tubing commonly used in such sets, and as a result the use of such pumps has been limited to applications requiring less critical flow rate control such as blood processing.
In the course of operation of a peristaltic pump the tubing on which the pump acts is subjected to repeated stretch-compression cycling. Because of its partial non-resiliency, tubing formed of vinyl and other thermoplastic materials may permanently change its shape and size with time as a result of such cycling, with the result that the rate at which fluidis delivered by the pump may be undesirably varied. Prior art peristaltic-type pumps have employed follower pins, rollers, pinchers, or similar means, to bear against the edges of the deformed tubing following compression to attempt to restore the tubing to its original shape, but these methods have had only limited success.
Another problem which arises with the use of peristaltic-type pumps in conjunction with fluid infusion sets is that should a failure of the tubing occur, or should the tubing be accidentally removed from the pump, the possibility of uncontrolled gravity flow of fluid into the body exists. Furthermore, dissolved gases in a liquid being infused may be released as bubbles as the liquid is subjected to pressure and/or temperature changes as it passes through the peristaltic pump. These bubbles may coalesce and form larger bubbles or pockets of gas which may be infused along with the liquid into the body, which may be harmful or even fatal to the patient under certain circumstances.
To prevent gas from being infused sensors may be located below the discharge end of the pump to automatically stop the pump should gas be detected or should the flow of fluid be interrupted. While such sensors are effective in preventing the infusion of gas, the stoppage of the infusion process they cause may itself be a risk to a critically ill patient, necessitating the continuous availability of medical personnel to re-establish the process.
The present invention is directed to a system for infusing fluid which provides improved fluid rate control by minimizing physical and dimensional changes in the tubing, minimizes the release of dissolved gases from the fluid, and guards against uncontrolled fluid flow should the pump fail or be inadvertently removed.
Prior art peristaltic pumps have typically included a plurality of rollers or the like against which the tubing is compressed by means of a spring-biased pressure plate so that as the rollers are advanced along the plate the tubing is repeatedly compressed and released to cause fluid to flow through the tubing. In such pumps, the number of rollers in compressive contact with the tubing varies as the rollers are advanced, so that, for example, at one point in time two rollers may compress the tubing, and at another time, one roller may compress the tubing. Since the rollers act on a common pressure plate, the compression force exerted on the tubing by any one roller varies as the number of rollers compressing the tubing varies. If the compression force varies too widely, for instance at a 2:1 ratio, the vinyl tubing commonly used in infusion sets may be caused to deform rapidly, stretch, extrude, and possibly even break open. The ultimate result could be a drop in or loss of fluid flow rate with possible harm to the patient.
The present invention is further directed to an improved peristaltic-type pump for use in conjunction with fluid infusion systems which provides a uniform compression force on an associated tubing segment, regardless of the number of points at which the tubing segment is being compressed.
Accordingly, it is a general object of the present invention to provide a new and improved fluid infusion system.
It is another object of the present invention to provide a new and improved system for infusing fluids into the human body which provides more accurate metering and improved pump efficiency.
It is another object of the present invention to provide a new and improved system for infusing fluids into the human body which provides improved protection against uncontrolled flow of fluid through the system.
It is another object of the present invention to provide a new and improved peristaltic pump which maintains a uniform compression force on an associated length of tubing regardless of the number of points at which the tubing is compressed.